Computer Systems Nat 4/5 Computing Science Computer Structure: Lesson 5: Computer Architecture

Lesson Aims By the end of this lesson: Pupils at will be able to: Label a computer system in terms of a 5 block diagram Describe the phrase ‘word length’ Describe the purpose of a processor List and describe the parts of a processor: Control Unit, ALU, registers Describe what a bus is and does

Computer architecture Computer architecture = the structure of a computer system Hardware = Physical parts of a computer system Device = One item of hardware Computer system has:- a processor Input device(s) Output device(s)

Computer architecture Nat 4/5 Computer architecture Storage Devices Output Devices Input Devices Processor Memory (RAM & ROM)

Typical desktop system Nat 4/5 Typical desktop system Processor - Carries out instructions Input Devices - Used to enter data e.g. keyboard and mouse Output Devices - Generate output e.g. monitor, printer. Memory - Stores programs and data - RAM and ROM Storage devices Store permanent copies of files.e.g. hard disk drive, DVD-Rewriter

Nat 4/5 The Processor Program / software = a set of instructions that tell the computer what to do The processor is the ‘brain’ of the computer – but can’t think just carries out instructions 1 chip Small piece of silicon

Stored program Instructions are stored in memory Processor fetches one instruction at a time from memory and carries it out Different programs allow the processor to carry out different tasks

Arithmetic and Logic Unit (ALU) Parts of a processor Processor Control Unit Arithmetic and Logic Unit (ALU) Registers

Control Unit Controls other parts of the processor Nat 5 Control Unit Controls other parts of the processor Makes sure that instructions are carried out in the correct order

Arithmetic and Logic Unit (ALU) Carries out calculations Makes decisions (logical operations) e.g. deciding one a number is the same or less than another number is a logical operation

Registers Storage locations inside the processor Hold:- data being processed instructions being executed memory addresses being accessed Small amount of storage space compared to RAM – does not hold a whole program - just the instructions being executed

Memory Memory contains many storage locations Each storage location has a unique address 2 types of memory chips as in a computer:- RAM and ROM

RAM – Random Access Memory Stores instructions and data that the computer is currently using Holds data while the computer is switched on - contents are lost when the computer is switched off User’s data stored in RAM

Read Only Memory Stores programs and data permanently - contents are not lost when the computer is switched off Programs are stored in ROM chips when the computer is manufactured Stores part of the Operating System

Buses Bus = a set of wires that connects parts of the computer e.g. memory and input/output devices Every computer has these buses:- Address bus Data bus Control bus

Buses Control Unit RAM Registers Nat 5 Buses Control Bus Processor Main Memory Control Unit RAM Data Bus ALU ROM Registers Address Bus A bus is a collection of wires which connect parts of the computer

Nat 5 Data Bus Carries data between the processor, memory and other parts of the computer e.g. input and output devices Bi-directional – data can travel in either direction on the data bus 64 wires in the data bus 16 wires in the data bus

Address Bus Address of a storage location = a binary number Address bus carries this information from the processor to memory to identify the location being accessed Uni-directional – data only travels from the processor to memory

Control Bus Consists of separate wires – each with it’s own function Clock line - regularly pulses with electricity to control the speed of the processor e.g. 3.6 GHz Read line – used when the processor is about to read from memory Write line – used when the processor is about to write data to memory

Summary The Processor has 3 main parts:- Nat 5 Summary The Processor has 3 main parts:- Control Unit Controls the timing and order of execution of instructions Arithmetic and Logic Unit (ALU) Performs the arithmetical and logical functions Registers Store information Buses connect parts of the computer:- Address bus – carries address of location being accessed Data bus – carries data Control bus – separate wires with their own job to ensure things happen at the correct time

Questions What is computer architecture? What is hardware? What is a device? What is software another name for? Name five parts of a computer system. Which part of the processor:- carries out sums and makes decisions? controls when instructions are fetched and executed stores data, addresses or instructions

More questions Name 2 types of memory chip. What are computer buses (include what a bus does). Name 3 buses.